The were built for the Imperial Japanese Navy during World War II. Both ships of the class were originally laid down as luxury passenger liners before being acquired by the IJN for conversion to aircraft carriers in 1941. Junyō was the first of the sisters to be completed in May 1942 and the ship participated in the invasion of the Aleutian Islands the following month. Both ships participated in several battles during the Guadalcanal Campaign in late 1942. Their aircraft were disembarked several times and used from land bases in a number of battles in the South West Pacific.